Why this economic crisis then?

The reason behind the crisis we are all enduring today is essentially one: debt. In particular, government debt.

In the past, economists like John M. Keynes promoted the idea that governments should encourage private investments during economic slumps in order to avoid recessions.
How?
By giving companies generous loans at cheap interest, that is, cheap price, which can be paid back once the economic slump is over.

At a first glance, there seems to be no danger at all in this procedure. History, however, has proved the opposite.